The present invention relates to a selective VP (Virtual Path) protection method, and in particular, to a selective VP protection method for performing protection of virtual paths in an ATM network comprising; a plurality of ATM cross-connect nodes, selectively employing VP end protection (VP protection executed by VP end nodes) and arbitrary type of VP protection executed by ATM cross-connect nodes other than the VP end nodes, in which an area of the VP-AIS (Alarm Indication Signal) cell transmitted by ATM cross-connect nodes which detected failure is utilized as information for selecting and determining the VP protection method.
Various kinds of VP protection methods (i.e. methods for protecting virtual paths established between VP end nodes) in ATM networks composed of a plurality of ATM cross-connect nodes have been proposed.
FIGS. 1 and 2 are schematic diagrams showing a general conventional VP protection method in an ATM network system. The ATM network system shown in FIGS. 1 and 2 comprises six ATM cross-connect nodes XC11xcx9cXC16 and ATM transmission lines connecting the ATM cross-connect nodes XC11xcx9cXC16. In the ATM network system of FIGS. 1 and 2, the ATM cross-connect nodes XC11 and XC 12, XC12 and XC13, XC13 and XC14, XC14 and XC15, XC15 and XC11, XC12 and XC16, and XC16 and XC13 are connected by the ATM transmission lines.
FIG. 1 is conceptually showing a case where a line failure 23 such as disconnection of optical fibers etc. occurred on the transmission line between the ATM cross-connect nodes XC12 and XC13 when a virtual path connection XC11-XC12-XC13-XC14 is established between the ATM cross-connect nodes XC11 and XC14.
The ATM network system composed of the ATM cross-connect nodes XC11xcx9cXC16 employs both VP end protection (VP protection executed by VP end nodes) and arbitrary VP protection. Here, the VP end protection means VP protection which is executed by VP end nodes of a virtual path. At present, the VP end protection can be classified into the following types.
I. pre-planned VP end protection
{circle around (1)} dedicated resources VP end protection
(with preset alternative routes and bandwidths)
{circle around (2)} semi-dedicated resources VP end protection
(with preset alternative routes)
II. real time restoration VP end protection
(or on-demand resources VP end protection)
The VP end protection executed by the VP end nodes XC11 and XC14 in FIGS. 1 and 2 includes the above three types of VP end protection. The arbitrary VP protection means arbitrary type of VP protection in its literal sense which is spontaneously executed by adjacent ATM cross-connect nodes other than the VP end nodes. The arbitrary VP protection includes APS (Automatic Protection Switching) which is employed in SDH (Synchronous Digital Hierarchy) and xe2x80x98section protection switchingxe2x80x99 which will described below, for example.
The VP end protection is executed between the ATM cross-connect nodes (VP end nodes) XC11 and XC14 using a route XC11-XC15-XC14 as an alternative route of the route XC11-XC12-XC13-XC14, and the arbitrary VP protection is executed between the ATM cross-connect nodes XC12 and XC13. In the case where the section protection switching is executed as the arbitrary VP protection between the ATM cross-connect nodes XC12 and XC13, a route XC12-XC16-XC13 is used as an alternative route of the route XC12-XC13.
FIG. 2 is conceptually showing a case where a node failure 24 occurred at the ATM cross-connect node XC12 when a virtual path connection XC11-XC12-XC13-XC14 is established between the ATM cross-connect nodes XC11 and XC14. The node failures are roughly classified into equipment failures such as breakage of optical transmitting devices (laser diodes etc.) and control abnormality such as a failure of routing LSI.
In the following, the conventional VP protection method in the ATM network system of FIGS. 1 and 2 employing both the VP end protection and the arbitrary VP protection will be described.
When the line failure 23 occurred on the transmission line XC12-XC13 as shown in FIG. 1, the arbitrary VP protection 32 is executed between the ATM cross-connect nodes XC12 and XC13 which detected the line failure 23. In the case where the section protection switching is executed as the arbitrary VP protection 32, the alternative route XC12-XC16-XC13 is used instead of the route XC12-XC13 and thereby communication between the VP end nodes XC11 and XC14 is secured via the route XC11-XC12-XC16-XC13-XC14. Incidentally, in the case where the transmission line XC12-XC13 includes xe2x80x98workxe2x80x99 and xe2x80x98standbyxe2x80x99 signal lines and the line failure 23 occurred on a work signal line between the ATM cross-connect nodes XC12 and XC13, the ATM cross-connect nodes XC12 and XC13 can execute switching from the work signal line to the standby signal line according to the APS, instead of the section protection switching. FIG. 1 is showing a case where the section protection switching is executed by the ATM cross-connect nodes XC12 and XC 13, for example.
On the other hand, when the node failure 24 occurred at the ATM cross-connect node XC12 as shown in FIG. 2, the VP end protection 33 is executed between the ATM cross-connect nodes XC11 and XC14 which are the VP end nodes of the virtual path connection XC11-XC12-XC13-XC14. In the VP end protection 33, the alternative route XC11-XC15-XC14 is used instead of the route XC11-XC12-XC13-XC14 and thereby communication between the VP end nodes XC11 and XC14 is secured via the route XC11-XC15-XC14.
An example of pre-planned VP end protection method is disclosed in Japanese Patent Application Laid-Open No. HEI8-237253 xe2x80x98METHOD AND APPARATUS FOR VIRTUAL PATH SWITCHING IN ATM NETWORKxe2x80x99. In the method, an operating virtual path and a standby (spare) virtual path are doubly set between two VP end nodes and virtual path switching from the operating virtual path to the standby virtual path is executed by the VP end nodes in the case of failure. In the VP end protection method, an OAM (Operation And Maintenance) cell, including an switching instruction code for indicating the presence/absence of switching request and a sequence number, is used for controlling the virtual path switching. The transmitting end node transmits the switching control OAM cells periodically on both of the operating virtual path and the standby virtual path, and the receiving end node detects the phase difference between the switching control OAM cells supplied via the two virtual paths by comparing the sequence numbers included in the switching control OAM cells. If the switching instruction code requesting virtual path switching included in the switching control OAM cell reached the receiving end node via the standby virtual path in perfect form, the virtual path switching from the operating virtual path to the standby virtual path is performed compensating the detected phase difference. By the VP end protection method, the switching to the standby virtual path can be executed without instantaneous chopping (i.e. maintaining synchronization of ATM cell timing between the operating and standby virtual paths) and with confirmation of normal operation of the standby virtual path.
Another example of pre-planned VP end protection method is disclosed in Japanese Patent Application Laid-Open No. HEI5-235983 xe2x80x98APPARATUS AND METHOD FOR VIRTUAL PATH SWITCHINGxe2x80x99. In the method, one or more alternative virtual paths are predetermined corresponding to a work virtual path, and information about the alternative virtual paths are prestored in an alternative virtual path information storing means of a virtual path switching device of each switching end nodes. The virtual path switching device of each switching end nodes further includes a virtual path capacity management means for storing and managing the capacity of the work virtual path, and a link capacity management means for storing and managing the capacities of links which are connected to the switching end node. When a failure is detected by a switching node, the node modifies its routing table into an alternative virtual path according to information which is stored in the alternative virtual path information storing means, the virtual path capacity management means and the link capacity management means, and transmits a switching control signal including information about the virtual path capacity and virtual path identifier to the adjacent node on the alternative virtual path. Each node on the alternative virtual path which received the switching control signal selects a link containing the alternative virtual path from links which are connected to the node according to the information in the switching control signal, and transmits the switching control signal to the next node on the alternative virtual path. Another switching end node of the alternative virtual path which received the switching control signal via the alternative virtual path executes switching control of ATM cell transmission route from the work virtual path with failure to the alternative virtual path according to the information included in the switching control signal. According to the method, the switching control signal is transmitted on the alternative virtual path only and thus the amount of control signals necessary for the virtual path switching can be decreased, and the virtual path switching can be executed without control of a central control node. Therefore, the failure on the ATM network can be relieved with high speed.
The aforementioned conventional VP protection method in an ATM network system shown in FIGS. 1 and 2 employing both the VP end protection and the arbitrary VP protection involves the following problem. The VP end protection executed by the VP end nodes is started according to reception of VP-AIS cells which are transmitted from failure detecting nodes. However, the VP end nodes can not judge the presence or absence of the arbitrary VP protection executed on the route between the VP end nodes, by information of the VP-AIS cell according to the present standard VP-AIS cell format. Thus, even in the case where a line failure on the route can be relieved immediately by means of the arbitrary VP protection, the VP end protection is started by the VP end nodes.
Referring to FIG. 4 for example, when the line failure 23 occurred on the transmission line XC12-XC13, the arbitrary VP protection is executed between the failure detecting nodes XC12 and XC13. However, the VP end protection 33 is started by the VP end nodes XC11 and XC14 according to the reception of the standard VP-AIS cells transmitted by the failure detecting nodes XC12 and XC13. Thus, even in the case where the line failure 23 can be relieved immediately by means of the arbitrary VP protection 32, the VP end protection 33 is started by the VP end nodes XC12 and XC13, thereby immediate relief by the arbitrary VP protection 32 is prevented.
The above problem occurs since the conventional VP end protection is started by the VP end nodes according to reception of the standard VP-AIS cells in which information about the presence or absence of the arbitrary VP protection executed between the VP end nodes is not included.
At present, there has been proposed no selective VP protection method employing both the VP end protection and the arbitrary VP protection selectively, which can provide high efficiency of VP protection and high compatibility between the VP end protection and the arbitrary VP protection.
It is therefore the primary object of the present invention to provide a selective VP protection method in an ATM network employing both the VP end protection and the arbitrary VP protection selectively, which can provide both high efficiency of VP protection and high compatibility between the VP end protection and the arbitrary VP protection.
In accordance with a first aspect of present invention, there is provided a selective VP protection method for protecting a virtual path connection established between VP end nodes in an ATM network which is composed of a plurality of ATM cross-connect nodes, employing both VP end protection and arbitrary VP protection selectively. In the selective VP protection method, the VP-AIS cell which is transmitted downward by each failure detecting node is composed including an area for carrying a switching flag which indicates the presence or absence of execution of the arbitrary VP protection by the failure detecting nodes. When an ATM cross-connect node capable of executing the arbitrary VP protection detected a line failure, the failure detecting ATM cross-connect node determines whether or not it executes the arbitrary VP protection in order to relieve the line failure, and transmits downward the VP-AIS cell in which the switching flag has been set according to the determination. The VP end node which received the VP-AIS cell refers to the switching flag and executes the VP end protection if the switching flag indicated the absence of execution of the arbitrary VP protection by the failure detecting nodes.
In accordance with a second aspect of present invention, in the first aspect, the failure detecting ATM cross-connect node determines to execute the arbitrary VP protection if it judged that the line failure can be relieved by the arbitrary VP protection by the failure detecting ATM cross-connect nodes.
In accordance with a third aspect of present invention, in the first aspect, the area for carrying the switching flag is placed in unusual octets of the standard VP-AIS cell format.
In accordance with a fourth aspect of present invention, in the third aspect, the area for carrying the switching flag is a 1-bit area.
In accordance with a fifth aspect of present invention, in the first aspect, the VP end node executes dedicated resources VP end protection as the VP end protection.
In accordance with a sixth aspect of present invention, in the first aspect, the VP end node executes semi-dedicated resources VP end protection as the VP end protection.
In accordance with a seventh aspect of present invention, in the first aspect, the VP end node executes real time restoration VP end protection as the VP end protection.
In accordance with an eighth aspect of present invention, in the first aspect, the failure detecting ATM cross-connect node executes APS (Automatic Protection Switching) as the arbitrary VP protection.
In accordance with a ninth aspect of present invention, in the first aspect, the failure detecting ATM cross-connect node executes section protection switching as the arbitrary VP protection.